1. Field of the Invention
The present invention relates to repair of semiconductor masks and reticles. More specifically the present invention relates to the use of a focused ion beam system which is capable of delivering, from a single ion beam column, several different species of ion beams, each of which is individually optimized to meet the differing requirements of the major functions to be performed in mask repair. These major functions are, mask imaging, which is the creation of an image of the microscopic structure of a region on the surface of a mask in order to locate the mask defect to be repaired; opaque defect repair which is the removal of material from the regions on the surface of the mask substrate where such material should be absent; and clear defect repair which is the deposition of opaque material onto undesired clear areas on the surface of the mask substrate.
2. The Prior Art
It is known to repair defects in photomasks by use of light and laser light. See for example U.S. Pat. No. 3,748,975 to Tarabocchia; U.S. Pat. No. 4,200,668 to Segal, et al.; PTC Application W081/03628 to Campy.
The use of light or laser light for the repair of semiconductor masks and reticles, while functioning adequately in some environments, presents problems, especially when smaller geometries, i.e., less than one micron, are encountered. The trend today in semiconductor circuit design is for increasingly smaller featured size, and the use of lasers for mask repair becomes disadvantageous because of the inability to focus the laser beam adequately to work with the smaller geometries, and because of the undesirable heating the laser beam causes in areas adjacent to the repair area.
The use of focused ion beams for mask repair is known. See, e.g., Wagner, Applications of Focused Ion Beams to Microlithography, Solid State Technology, May, 1983. Such prior art systems known to the inventors utilize a single ion beam species.
Representative of the prior art devices are the KLA/Micrion 808 and the Sieko SIR 1000 systems. Both systems are capable of delivering only a single type of focused ion beam species to the mask under repair, namely a gallium beam of between 35 to 50 keV in energy. Such a beam produces significant mask damage during imaging due to the beam's high sputter rate. In addition, significant amounts of gallium are implanted into the mask substrate during imaging and opaque defect repair, resulting in an effect called "gallium staining". This effect causes local reductions of the substrate's transparency which are prone to later identification as defects by industry-standard mask inspection equipment.
It is also known to repair clear defects by inducing deposition of an adherent carbon film from a hydrocarbon gas onto the mask surface by use of a focused ion beam. See, e.g., Submicron Mask Repair Using Focused Ion Beam Technology, SPIE, Vol. 632, Electron-Beam, X-Ray & Ion Beam Techniques For Submicrometer Lithographies V (1986).
While these prior art methods and systems attempt clear defect repair differently, they do not deposit into the clear defects a material compatible with the pre-existing metallic film forming opaque portions of the mask. Additionally, the Sieko system uses a chemical vapor deposition process which complicates system design and facilities requirements, whereas the KLA/Micrion system sputter etches the mask substrate with a gallium beam, which is very slow process and is irreversible.